Define close resource not to return an error

There is nothing the pool can do on an error. If the client code
wishes to handle or log errors it can do so in the close resource
function.

This removes the need for background error reporting.

pool_test.go

@@ -60,18 +60,16 @@ func createCreateResourceFuncWithNotifierChan() (puddle.CreateFunc, *Counter, ch
 func createCloseResourceFuncWithNotifierChan() (puddle.CloseFunc, *Counter, chan int) {
 	ch := make(chan int)
 	var c Counter
-	f := func(interface{}) error {
+	f := func(interface{}) {
 		n := c.Next()
 
 		// Because the tests will not read from ch until after the close function f returns.
 		go func() { ch <- n }()
-
-		return nil
 	}
 	return f, &c, ch
 }
 
-func stubCloseRes(interface{}) error { return nil }
+func stubCloseRes(interface{}) {}
 
 func waitForRead(ch chan int) bool {
 	select {
@@ -233,9 +231,8 @@ func TestPoolCloseClosesAllAvailableResources(t *testing.T) {
 	createFunc, _ := createCreateResourceFunc()
 
 	var closeCalls Counter
-	closeFunc := func(interface{}) error {
+	closeFunc := func(interface{}) {
 		closeCalls.Next()
-		return nil
 	}
 
 	p := puddle.NewPool(createFunc, closeFunc)
@@ -356,56 +353,6 @@ func TestPoolGetReturnsErrorWhenPoolIsClosed(t *testing.T) {
 	assert.Nil(t, res)
 }
 
-func TestPoolCloseResourceCloseErrorIsReported(t *testing.T) {
-	createFunc, _ := createCreateResourceFunc()
-	errCloseFailed := errors.New("close failed")
-	closeFunc := func(res interface{}) error { return errCloseFailed }
-	pool := puddle.NewPool(createFunc, closeFunc)
-	asyncErrChan := make(chan error, 1)
-	pool.SetBackgroundErrorHandler(func(err error) { asyncErrChan <- err })
-
-	// Get and return a resource to put something in the pool
-	res, err := pool.Get(context.Background())
-	require.NoError(t, err)
-	assert.Equal(t, 1, res)
-	pool.Return(res)
-
-	pool.Close()
-
-	select {
-	case err = <-asyncErrChan:
-		assert.Equal(t, errCloseFailed, err)
-	default:
-		t.Fatal("error not reported")
-	}
-}
-
-func TestPoolReturnClosesResourcePoolIsAlreadyClosedErrorIsReported(t *testing.T) {
-	createFunc, _ := createCreateResourceFunc()
-
-	errCloseFailed := errors.New("close failed")
-	closeFunc := func(res interface{}) error { return errCloseFailed }
-	pool := puddle.NewPool(createFunc, closeFunc)
-
-	asyncErrChan := make(chan error, 1)
-	pool.SetBackgroundErrorHandler(func(err error) { asyncErrChan <- err })
-
-	// Get and return a resource to put something in the pool
-	res, err := pool.Get(context.Background())
-	require.NoError(t, err)
-	assert.Equal(t, 1, res)
-
-	pool.Close()
-
-	pool.Return(res)
-	select {
-	case err = <-asyncErrChan:
-		assert.Equal(t, errCloseFailed, err)
-	case <-time.NewTimer(time.Second).C:
-		t.Fatal("timed out waiting for async error")
-	}
-}
-
 func BenchmarkPoolGetAndReturn(b *testing.B) {
 	benchmarks := []struct {
 		poolSize              int